The present invention generally relates to an implantable therapy system. The present invention more particularly relates to such a system wherein the administration of therapy is electronically controlled by a control module and wherein a therapy module that delivers a given therapy is physically separate from the control module.
Implantable therapy delivery systems have been in the art and in commercial use for decades. Such systems include cardiac rhythm management systems such pacemakers and defibrillators, nerve stimulators, and even drug delivery systems.
Such therapy systems, and especially in the case of cardiac rhythm management and nerve stimulator systems, include an implantable device that includes a power source, such as a battery and electronic circuitry that generates therapy stimulation pulses and controls when the therapy stimulation pulses are delivered. To actually deliver the stimulation pulses, the systems also generally include multiple stimulation electrodes on the surface of a lead that make electrical contact with the desired (target) tissue and a lead system, including one or more leads that connect the electrodes to the electronic circuitry in the device.
As implantable therapy device design has progressed over time, more and more functionality has been incorporated into the implantable devices and more and more electrodes have been similarly required to shape stimulation at the target tissue volume to enable that functionality. For example, implantable therapy devices usually now incorporate microcontrollers that are capable of controlling multiple therapy delivery modalities in multiple locations of the body. Those modalities may include both stimulation pulse delivery to selected tissue(s) and/or physiologic activity monitoring and data gathering for analysis and adjustment of therapy. In the case of nerve stimulation systems, these systems now find use in various locations of the body as for example, in brain tissue stimulation and spinal nerve stimulation.
Particularly in nerve stimulators, there has been an increase in the number of electrodes assigned to shape and deliver electrical pulses to a given anatomical region. The intended advantage is to obtain stimulation selectivity and directionality and to shape current delivery to a volume of tissue. Today, a system may incorporate as many as sixteen to twenty electrodes in a given area. Unfortunately, current state of the art connectivity measures to connect the electrodes back to the implantable pulse generation devices have limited the number and utility of electrodes.
For example, each electrode requires an electrical conductor or wire to extend from the electrode through its associated lead and back to the implanted device. The large number of such conductors is limited by the amount of space available in a lead. Further, each conductor requires a hermetically sealed connection with the implanted device. This places a huge burden on feed through systems which can accommodate only a limited number required contacts and in effect, limits the number of electrodes to the constraints imposed by the connector.
Still further, the required higher density of conductors required for the increased number of electrodes results in smaller diameter conductors. The smaller diameter conductors present higher impedance conduction paths between the electrodes and the implantable devices. This results in higher required power output from the implantable electronic devices to deliver the desired effective stimulation therapy. The required higher power output also either decreases battery life of the implantable devices or requires larger batteries to be employed. The smaller diameter conductor wire would also exhibit reduced strength and flex life in locations where this results in reduced reliability of the cable lead. Such stresses at the lead/stimulator connections cause an unacceptably high rate of device failure.
As a further matter, some clinical applications of nerve stimulators require the location of the electrodes to be in locations where replacement of the electrodes would require surgery and impose increased clinical risk to the patient. Also, anchoring the lead can be an issue to prevent the dislodgement of electrode(s) by inadvertent body movement or pulling on the lead. For example, anchoring leads at the exit of the vertebrae for spinal cord stimulation has been a reliability limitation of current technology.
As may be seen from the foregoing, there is a need in the art for a different approach in providing therapy within a body where a control device must be connected to monitoring and therapy delivery elements such as sensing or pulse delivery electrodes. It would be desirable if such an approach would avoid high impedance conduction paths, minimize electrode dislodgement, prevent interconnection issues and increase the safety to and convenience of the patient. The present invention addresses these and other issues.